1. Field of the Invention
The present invention generally relates to a method of setting synchronous communication in a bus network such as an IEEE-1394 bus network in which plural buses are connected via a bridge, a bus network utilizing the method and a medium of an information provider. More particularly, the present invention relates to a method of setting synchronous communication in a bus network and others wherein, when the synchronous communication for a bus and a bridge respectively constituting a path (a communication channel) from a sending node to a receiving node is set, a request for setting synchronous communication from a resource-possessing node is sequentially propagated to enable the synchronous communication to be set satisfactorily, even if the resource-possessing node, the sending node and the receiving node do not exist on the same bus.
2. Description of Relevant Art
For a standard for transmitting a digital signal, multiple standards such as standards by International Electrotechnical Commission (IEC) and Institute of Electrical and Electronics Engineers (IEEE) exist. Above all, IEEE 1394 attracts attention in application to multimedia such as the connection between pieces of the electronic equipment for domestic use, for example, digital video recorder, and connection between these pieces of the electronic equipment and a computer. As IEEE 1394 is well-known, the description of the contents is omitted.
Currently, P1394.1 working group makes the protocol standardization activities of a bridge for connecting buses used in an IEEE-1394 high-speed serial bus communication environment (the working group has prepared a draft for standardization entitled P1394.1 Draft 0.03 Oct. 18, 1997 as of June in 1998). In the following description, the above latest draft for standardization is called a bridge draft. An IEEE-1394 bridge (hereinafter called only a bridge) is composed of two communication means connected thereto, each of which is called a portal, and is connected to an IEEE-1394 bus (hereinafter suitably abbreviated to a bus) . The data can be transmitted via the above bridge between plural buses.
The number of nodes (IEEE-1394 equipment) which can be connected to one IEEE-1394 bus is limited to a maximum of 63. However, the connection of the plural buses through the bridge to constitute bus network including buses and bridges allows it to connect the nodes of more than 63. It has been already proposed that data should be transmitted not only via a cable but using a radio wave, infrared rays and others in a bridge (between portals).
IEEE 1394 is provided with an isochronous transfer function and thus synchronous communication is executed on an IEEE-1394 bus every 125 xcexcsec. FIG. 1 shows an example in which an isochronous packet is transferred in synchronous communication. A node called a cycle master sends a cycle start packet CS every 125 xcexcsec. After the cycle start packet CS is sent, the transfer of an isochronous packet is started. In FIG. 1, two types of isochronous packets Pis are transferred using channels a and b. After the transfer of the isochronous packets Pis is completed, the transfer of an asynchronous packet Pas is started.
To enable the above synchronous communication, the setting of synchronous communication, that is, setting for channels and band capacity is required. However, in IEEE 1394, only a method of setting synchronous communication in a case that an owner (a resource-possessing node in synchronous communication), a talker (a packet sending node in synchronous communication) and a listener (a packet receiving node in synchronous communication) are connected to the same bus, is defined. That is, a method of setting synchronous communication in case an owner, a talker and a listener exist on different buses is undefined. In the IEEE-1394.
The object of the present invention is to provide a method of setting synchronous communication and others in a bus network in which the setting of synchronous communication is satisfactorily enabled even if a resource possessing node, a sending node and a receiving node are not connected to the same bus.
A method of setting synchronous communication in a bus network according to the present invention is a method in which a plurality of the buses are connected to each other using a bridge including first and second communication means and is provided with the following first to third steps.
In the first step, a resource-possessing node sets synchronous communication for a first bus when a sending node or a receiving node exists on the first bus on which the resource-possessing node itself exists, and the resource-possessing node sends a request for setting synchronous communication to the first communication means of the bridge existing on the first bus when no sending node or no receiving node exists on the first bus and passing a packet to the sending node or the receiving node respectively not existing on the first bus.
In the second step, the first communication means of the bridge received the request for setting synchronous communication from the resource-possessing node sends a request for setting synchronous communication to second communication means connected to the first communication means, and sets synchronous communication for the first communication means itself when the first communication means itself is existed on a path from the sending node to the receiving node.
In the third step, the second communication means of the bridge received the request for setting synchronous communication sets synchronous communication for a second bus when the above sending node or the above receiving node exists on the second bus on which the second communication means itself exists, sets synchronous communication for the second communication means itself when the second communication means itself exists on a path from the sending node to the receiving node and further sends a request for setting synchronous communication to the first communication means of the bridge existing on the second bus when no sending node or no receiving node exists on the second bus and passing a packet to the sending node or the receiving node respectively not existing on the above second bus.
In the present invention, after the first step is executed, the second and third steps are suitably repeated. A request for setting synchronous communication is sequentially propagated and synchronous communication is set for buses and a bridge constituting a path from a sending node to a receiving node. Whereby, even if a resource-possessing node, a sending node and a receiving node do not exist on the same bus, the setting of synchronous communication is satisfactorily executed.
A further understanding of the nature and advantages of the invention may be realized by reference to the following portion of the specification and drawings.